Microbial growth occurs in many systems in which aqueous media such as water, aqueous solutions and aqueous dispersions of material are employed.
For example, there is a significant biofouling problem in many areas of photoprocessing and other systems, in particular where low flowrate washes and water recycling is employed. Biofouling is a complex process which causes microorganisms e.g. bacteria to attach to surfaces and can occur over a wide range of bacterial levels. This may be due to a diffusion controlled process or the lack of food in solution encouraging the bacteria to attach to surfaces.
Biocides have been used for many years to control biogrowth but have several drawbacks. First, they are by nature fairly toxic chemicals and thus present handling and containment problems. Secondly, addition of biocides is not often controlled carefully and they can be added when not needed which is costly and potentially harmful to the environment. Thirdly, microorganisms can become resistant to a particular biocide which necessitates switching biocides at regular intervals. Fourthly, legislation on discharges to drains is becoming more stringent in many countries such that the levels of biocide disposal may become an issue preventing their conventional use. Finally, there is no universal treatment to kill or control all types of bacteria and fungi. Hence, the prior art is limited to these relatively toxic chemicals, chlorination, UV, ozonolysis and gamma radiation.
EP-A-0 536 087 describes a resevoir system for the prolonged and even release of soluble active materials into water or an aqueous medium which comprises a nonwoven fabric bag containing the active material e.g. an antifungal agent. The nonwoven material is made from continuous monofilaments or microfibres of a synthetic thermoplastic polymer which has been treated to give it the required degree of permeability.